Treatment of manganese-containing materials

ABSTRACT

An improved method for treating manganese-containing materials, such as seafloor manganese nodules, by leaching with aqueous HNO 3  and NO gas, and more particularly to methods for recovering valuable constituents from such nodules, especially manganese, cobalt, nickel, iron, and copper. It also provides a method to leach manganese material to release the titanium, vanadium, cerium, molybdenum and other metals from the manganese oxides and to make them available to be recovered.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of PCT ApplicationPCT/US13/23777, filed Jan. 30, 2013, and U.S. Provisional PatentApplications Ser. No. 61/593,107, filed Jan. 31, 2012, and 61/681,193,filed Aug. 9, 2012.

FIELD OF THE INVENTION

The present invention relates to a method for treatingmanganese-dioxide-containing materials, The invention is well suited totreating manganese-containing nodules recovered from the seafloor orlake floor, as well as manganese ores. The invention relatesparticularly to methods for leaching and recovering valuableconstituents from such materials, especially manganese, and, if present,cobalt, nickel, copper, iron, and other valuable metals.

BACKGROUND OF THE INVENTION

Manganese-containing material treated by the invention can includemanganese dioxide minerals in any form, including ores, or nodules, suchas deep sea nodules.

Polymetallic or manganese nodules, are concretions formed of concentriclayers of iron and manganese oxides around a core.

Deep sea nodules on the ocean floor include in their composition atleast manganese (Mn) and usually nickel, cobalt, copper, zinc, and iron,with small amounts of titanium, vanadium, molybdenum, and cerium. Oftenpresent in addition are one or more of the following metals: magnesium,aluminum, calcium, cadmium, potassium, sodium, zirconium, titanium,lead, phosphorus, and barium.

All of the desired valuable metals in manganese nodules are tied up withinsoluble oxidized manganese, such as MnO₂. Only about 5% of themanganese contained in the nodules is acid soluble. Thus it is necessaryto reduce the MnO₂ by a suitable reducing agent as a first step in orderto recover the metal constituents. Historically, SO₂ has been used forthis purpose. For deep sea nodules, carbon monoxide has also been used.However such prior art processes often do not recover a suitablemanganese product, are capable of recovering only from about 80 to about92% of the primary metal values, and often produce large quantities ofwaste. Moreover, a sulfate system requires large sized equipment withattendant high capital cost.

Unexpectedly, and contrary to earlier teachings, it has been found thatreacting manganese-dioxide-containing materials with nitric oxide in thepresence of nitric acid in aqueous solution results in recovery of atleast 99% of the manganese values and associated metals (known as “paymetals” because they have higher commercial value than manganese).

SUMMARY OF THE INVENTION

The present invention is a process for recovering manganese and, ifpresent, other metal values from manganese-containing material,including deep sea manganese nodules, by treating manganese-containingmaterial with nitric oxide (NO) in an aqueous nitric acid solution. Thenet reaction with the MnO₂ is as follows:

3MnO₂+2NO+4 HNO₃->3Mn(NO₃)₂+2H₂O

liberating the trapped desired valuable metals. In the present process,the quantity of NO required per unit of manganese recovered is less thanone-third of the quantity of SO₂ required per unit of manganese, or thequantity NO₂ required per unit of manganese. Thus, the invented processdelivers substantial savings in reactant costs and byproduct disposal.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide an improvedmethod of recovering manganese from manganese-bearing materials.

Another object of the invention is to provide an effective leach forrecovering metal values from manganese-bearing materials, including, ifpresent, nickel, cobalt, zinc, copper, magnesium, aluminum, iron,cadmium, zirconium, titanium, lead, cerium, molybdenum, phosphorus,barium, and vanadium.

Another object of the invention is to provide an effective method ofrecovering metal values from undersea manganese-containing materialsincluding deepsea manganese nodules.

Another object of the invention is to produce fertilizer grade nitratematerials.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects will become more readily apparent byreferring to the following detailed description and the appendeddrawings, in which.

FIG. 1 is a schematic flow sheet of the invented process.

FIG. 2 is a schematic flow sheet of a more detailed process to theprocess depicted in FIG. 1.

DETAILED DESCRIPTION

Referring now to FIG. 1, the invented method of recovering manganesefrom materials 10 containing manganese-dioxide and other metal values,comprises the steps of:

-   -   a. leaching 12 the manganese-dioxide containing materials with        HNO₃ and NO gas in an aqueous solution to form MnO which        dissolves in the nitric acid, releases the accompanying metals        into solution, and leaves an acid-insoluble, essentially metal        free residue;    -   b. precipitating 14 iron from the solution as a residue;    -   c. separating 16 the iron-containing residue 18 from the        solution; and    -   d. precipitating and recovering manganese 20 from the solution.

The process begins with manganese-containing material, such as deepseamanganese nodules, which may be obtained from an ocean, sea, or otherbody of water. Sometimes such nodules are found in large lakes. The deepsea nodules often contain in excess of 20 percent manganese, usuallyabout 30 percent.

In addition to manganese, such deep sea nodules usually contain at leastone of the following metals: nickel, cobalt, zinc, copper, magnesium,aluminum, iron, calcium, cadmium, potassium, sodium, zirconium,titanium, lead, cerium, molybdenum, phosphorus, barium, and vanadium.The invented process includes the efficient leaching and recovery ofmany of these metal values.

Optionally, the nodules are crushed or ground to increase the surfacearea for leaching. Advantageously, any chlorides in the nodules, such asfrom salt water, are removed by any convenient method, such as washing.This step may be done before, during or after any crushing butpreferably after. Crushing or grinding the nodules can occur duringleaching in a wet mill or wet crusher.

Preferably, the nodules are leached in an aqueous nitric acid solutioninto which NO gas is introduced. Alternatively, the NO gas first may beintroduced into an aqueous HNO₃ solution, followed by the introductionof nodules into the solution to complete the reaction.

The NO reacts with MnO₂ to form MnO and NO₂, and to release the othermetals from the nodules. The MnO so produced dissolves in the nitricacid, leaving an acid-insoluble residue, which may be removed from thesolution at that time, or the acid-insoluble residue may be carriedforward to the iron-precipitation step and removed with the iron, asdesired. The temperature of the solution is preferably controlled to atemperature in the range of 30 to 120° C. to achieve the reaction.

The pH of the solution is then changed to about 0.5-2.5 to precipitatehydrated iron oxide. The precipitated iron values are removed bysolid-liquid separation techniques. This pH change may be achieved invarious ways, including the addition to the solution of a precipitatingagent, such as alkalis, alkaline earths, ammonia, or other acid-reducingagents. Alternatively, such precipitation can be effected by any othermethod of achieving iron hydrolysis and its precipitation, ensuring theseparation of iron from the more valuable metals.

Once in solution, the metal values may be precipitated as oxides orsulfides. Any copper, lead, cadmium, and zinc present in the solution isremoved therefrom. Preferably, the solution is adjusted to a low pH,preferably less than 3, and a heavy-metal precipitating agent, such as asulfide or an organic reagent or a complexing agent, is introduced intothe solution to precipitate any copper, lead, cadmium, and zinc which ispresent in the solution, and the precipitated metal values are removedby solid-liquid separation.

The pH of the solution is raised, and, if desired, a sulfide is added tothe solution to precipitate cobalt and nickel as sulfides. Remainingaluminum and some remaining zinc may also be precipitated as sulfides inthis step.

Preferably, the pH of the solution is then raised to a pH in the rangeof about 8 to 10 to precipitate manganese. After separating themanganese residue, the remaining solution is a fertilizer grade nitrateproduct. Alternatively, the manganese nitrate in the solution can bedecomposed to recover manganese oxide and nitrogen dioxide, the latterof which can be readily converted to nitric acid.

Referring now to FIG. 2, which depicts an embodiment of the presentinvention in greater detail than FIG. 1, the method of recovering metalvalues from deep-sea manganese nodules, comprises the steps of:

-   -   a. obtaining manganese-containing nodules 22 which also contain        at least one of the metals of the group consisting of: cobalt,        nickel, lead, copper, magnesium, aluminum, iron, cadmium,        zirconium, titanium, zinc, cerium, molybdenum, phosphorus,        barium, and vanadium;    -   b. leaching the nodules at 12 with HNO₃ and NO gas in an aqueous        solution to form manganese nitrate in solution and to release        the other metals into solution;    -   c. adding pH adjusting agents 24 to the solution 26 to        precipitate ferric hydroxide;    -   d. separating 28 the precipitated ferric hydroxide from the        solution;    -   e. adjusting 30 the solution to a low pH and introducing a        sulfide to the solution to precipitate copper, lead, cadmium,        and zinc 32, if present in the solution;    -   f. raising 34 the pH of the solution and introducing additional        sulfide to precipitate cobalt and nickel sulfides 36; and    -   g. raising the solution pH to about 8 to 10 to precipitate        hydrated manganese oxide product.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

From the foregoing, it is readily apparent that we have invented animproved method for treating manganese-containing material including thetreatment of seafloor manganese nodules recovered by undersea mining toeffectively leach the material to produce a manganese oxide product andrelease any valuable metals by reducing manganese dioxide with nitricoxide, and for recovering the metal values contained in the nodules moreefficiently and more economically than heretofore has been possible. Wehave also invented an improved method of recovering manganese frommanganese-bearing materials, including an effective leach for recoveringmetal values from manganese-bearing materials, including, if present,nickel, cobalt, copper, magnesium, aluminum, iron, cadmium, zirconium,titanium, zinc, lead, cerium, molybdenum, phosphorus, barium, andvanadium; as well as an effective method of recovering metal values fromundersea manganese-containing materials including deepsea manganesenodules, and for producing a fertilizer grade nitrate material.

It is to be understood that the foregoing description and specificembodiments are merely illustrative of the best mode of the inventionand the principles thereof, and that various modifications and additionsmay be made to the apparatus by those skilled in the art, withoutdeparting from the spirit and scope of this invention, which is definedby the appended claims.

What is claimed is:
 1. A method of recovering manganese from materialscontaining manganese-dioxide and other metal values, comprising thesteps of: a. leaching the manganese-dioxide containing materials withHNO₃ and NO gas in an aqueous solution to form MnO which dissolves inthe nitric acid and releases the accompanying metals into solution, andleaving an acid-insoluble residue; b. precipitating iron from thesolution as a residue; c. separating the iron-containing residue fromthe solution; and d. precipitating and recovering manganese from thesolution.
 2. A method according to claim 1 wherein themanganese-containing materials are leached in an aqueous nitric acidsolution into which nitric oxide gas is then introduced.
 3. A methodaccording to claim 1 wherein the manganese-containing material containsat least one of the metals of the group consisting of: nickel, cobalt,copper, magnesium, aluminum, iron, calcium, cadmium, potassium, sodium,zirconium, titanium, zinc, lead, cerium, molybdenum, phosphorus, barium,and vanadium.
 4. A method according to claim 1 wherein themanganese-containing materials are manganese nodules obtained from anybody of water, including a seafloor or lake floor.
 5. A method accordingto claim 4, further comprising removing chlorides from the nodules priorto leaching.
 6. A method according to claim 1 wherein themanganese-containing materials are dioxides or ores.
 7. A methodaccording to claim 4, further comprising crushing or grinding thenodules prior to leaching.
 8. A method according to claim 4, furthercomprising crushing or grinding the nodules during leaching in a wetmill or wet crusher.
 9. A method according to claim 5, wherein thechlorides are removed by washing the materials.
 10. A method accordingto claim 9, wherein the chlorides are removed by washing the materialsprior to leaching while crushing or grinding the nodules in a wet millor wet crusher.
 11. A method according to claim 1, further comprisingremoving the acid-insoluble residue prior to precipitating the iron. 12.A method according to claim 1 wherein following leaching, the pH of theleachant is changed to about 0.5-2.5 to precipitate hydrated iron oxide.13. A method according to claim 12 wherein the pH of the leachant ischanged by the addition to the solution of pH adjusting agents.
 14. Amethod according to claim 13 wherein the pH adjusting agents areselected from the group consisting of alkalis, alkaline earths, orammonia.
 15. A method according to claim 12 wherein the precipitatedferric hydroxide is removed from the solution by solid-liquidseparation.
 16. A method according to claim 1 where any copper, lead,cadmium, and any zinc present in the solution are removed byprecipitation at a low pH of less than 3.0, followed by solid-liquidseparation.
 17. A method according to claim 16 where precipitation iseffected by adjusting the solution to a pH of less than 3.0, thenintroducing a sulfide into the solution to precipitate as sulfides anycopper, lead, cadmium, and zinc which is present in the solution, andthe precipitated metal values are removed by solid-liquid separation.18. A method according to claim 1, further comprising raising the pH ofthe solution, precipitating and removing any cobalt or nickel.
 19. Amethod according to claim 18, wherein precipitation of cobalt and nickelis carried out by raising the pH of the solution and introducingadditional sulfide thereto, and forming cobalt and nickel sulfides insolid form.
 20. A method according to claim 1, wherein precipitation ofmanganese is carried out by raising the solution pH to about 8 to 10.21. A method according to claim 1 further comprising, after the finalstep in which the solution contains manganese nitrate, thermallydecomposing the manganese nitrate to form manganese dioxide and nitrogendioxide.
 22. A fertilizer grade nitrate product produced by the methodof claim
 1. 23. A method of recovering metal values from deep-seamanganese nodules, comprising the steps of: a. obtainingmanganese-containing nodules having a manganese content in excess of20%, and containing at least one of the metals of the group consistingof: cobalt, nickel, lead, copper, magnesium, aluminum, iron, cadmium,zirconium, titanium, zinc, cerium, molybdenum, phosphorus, barium, andvanadium; b. leaching the nodules with HNO₃ and NO gas in an aqueoussolution to form manganese nitrate and to release the other metals; c.adding pH adjusting agents to the solution to precipitate ferrichydroxide; d. separating the precipitated ferric hydroxide from thesolution; e. adjusting the solution to a low pH and introducing asulfide to the solution to precipitate copper, lead, cadmium, and zinc,if present in the solution; f. raising the pH of the solution andintroducing additional sulfide to precipitate cobalt and nickelsulfides; and g. raising the solution pH to about 8 to 10 to precipitatehydrated manganese oxide.